The invention relates generally to a drive system for an exercise treadmill and, more particularly, to a drive system for an exercise treadmill which includes a motor capable of producing usable torque from either an AC or DC power source.
Exercise treadmills are used by hospitals, health clubs and individuals to measure and/or improve the aerobic and cardiovascular fitness of the treadmill user. Such treadmills typically comprise a frame which supports an endless belt having an exposed, relatively flat top surface several feet in length to accommodate the walking, jogging or running stride of the user. The belt is mounted between two rollers which, in turn, are mounted to the frame by bearings. An electrically powered drive motor is typically connected to at least one of the rollers by a V-belt and pulley arrangement, or similar mechanism. On more sophisticated treadmills, some form of speed control is usually provided so that the speed of movement of the exercise surface of the endless belt can be varied.
Both AC and DC drive motors have been used in exercise treadmills found in the prior art. AC drive motors are relatively simple and inexpensive to produce, maintain and operate. An AC power source (e.g., 115 v.a.c., 60 Hz.) is normally readily available to the user, eliminating the need for and extra expense associated with transformers, rectifiers or other power conversion devices. However, smooth and efficient speed control over a wide operating range is more difficult to attain when using an AC motor. Moreover, the torque requirements in a treadmill are not uniform, but rather vary as the users feet make contact with and leave the exercise surface. The response of a DC motor to such torque changes is generally smoother and faster than is the response of an AC motor.
U.S. Pat. No. 4,643,418 shows an example of a treadmill which uses an AC motor to drive the endless belt. The speed of the belt is controlled by a speed control potentiometer or rheostat (54) which has a graduated scale to set the speed of the AC motor. The speed control must be set to its "off" or "zero" position when terminating an exercise session. If the speed control has not been turned to its "off" position, prior to turning on the main power switch to begin exercising, the treadmill will not respond. Depending upon the size of the resistance "steps" used, this type of speed control is incremental in nature. The power dissipated in the resistance element is wasted, lowering the efficiency of the overall system and creating a need to safely dissipate heat generated by the current flowing through the resistance element. Finally, AC motors are relatively noisy in operation. This problem is exacerbated if a larger motor must be used due to the inefficiency introduced by the speed control circuitry.
A number of treadmills utilize DC motors to drive the endless belt. DC motors are often preferred due to the ease with which DC motors may be speed controlled across a relatively wide range. U.S. Pat. No. 4,635,927 shows an exercise treadmill which uses a DC motor and a pulse width modulated control system to control motor speed. According to the specification of this patent, this arrangement allows the motor to operate at a relatively high efficiency across a wide range of motor speeds when compared to "traditional" treadmills which utilize AC induction motors. However, the treadmill described in U.S. Pat. No. 4,635,927 draws its power from a 110 v.a.c., 60 Hz. source, which requires that a rectifier and filter be employed to convert the incoming AC power to DC power prior to connecting the source to the motor. These rectifier and filter circuits are imperfect so that the power supplied to the DC drive motor is actually a mixture of AC and DC power. The AC component of the power source degrades the performance of the DC motor, resulting in a decrease in operating efficiency. The decrease in efficiency may require that a larger DC motor be provided to assure satisfactory performance of the treadmill. An increase in motor size results in noisier operation and an increase in the overall size of the space required to accommodate the drive mechanism.
U.S. Pat. No. 4,664,646 describes a treadmill motor drive which utilizes a thin, high speed, low torque motor to drive the endless belt of the treadmill. This arrangement is contrasted to "prior art" treadmill motor drives in which bulkier high torque, low speed motors are used. The small size and light weight of this unit are desirable in a treadmill which is intended to be folded up or transported from one location to another on a regular basis. Reductions in bulk and weight may, of course, be desirable in stationary treadmills as well.
Other examples of treadmills having electric motor driven mechanisms can be found in U.S. Pat. Nos. 3,602,502; 3,606,320; 3,711,812; 4,344,616; 4,374,587; 4,445,683; 4,602,779; 4,635,927; 4,749,181; and 4,842,266.
An object of the present invention is to provide an electric motor drive arrangement for a treadmill which is relatively efficient in operation.
Another object of the present invention is to provide an electric motor drive arrangement for a treadmill which is relatively small and compact in design.
Yet another object of the present invention is to provide an electric motor drive arrangement for a treadmill which is relatively quiet in operation.
Yet another object of the present invention is to provide an electric motor drive arrangement for a treadmill which can be powered by an imperfectly rectified AC power source, while suffering relatively little performance degradation due to the presence of the AC power component in the rectified source.
These and other objects of the present invention are attained in a drive arrangement for an exercise treadmill having a frame and an endless belt mounted within the frame, comprising electric drive means for driving the endless belt to provide a moving exercise surface, means for receiving electrical power from an AC power source, and rectifier means for rectifying the AC power to provide a power source for the electric drive means. The power source provided by the rectifier has both a DC component and an AC component. The electric drive means comprises an electric motor having a stator winding and an armature winding connected in series with each other and in parallel with (i.e., across) the output of the rectifier.
The electric motor comprises a laminated stator supporting the stator winding, a wound rotor, a commutator which is electrically connected to the wound rotor, and a pair of brushes in contact with the commutator. The stator winding and brush holders are serially connected to each other (i.e., one end of the stator winding is connected to one of the brush holders) and in parallel with the rectifier output (i.e., the other end of the stator winding and the other brush holder are connected across the rectifier output). The series connected electric motor is capable of producing torque for driving the endless belt from both the AC component and the DC component of the rectified electric power source. The motor is mounted by means of resilient mounting bushings to the frame of the exercise treadmill.
In one embodiment of the invention, the rectifier further includes a control system for controlling the rotational speed of the electric motor. The control system includes a motor speed measuring device which is mounted adjacent a rotating shaft of the electric motor. The measuring device is an electromagnetic tachometer providing a variable frequency signal.
The inventors have recognized that power supplies and rectifiers of the type commonly used in treadmills are imperfect. The rectified DC power, which is normally supplied to a DC motor, has an AC component which degrades the performance of the DC motor, resulting in motor inefficiencies, increased noise levels, and other disadvantages. The inventors have discovered that providing a series connected motor (sometimes referred to as a "universal" motor) which is powered from a source of the type typically used to power a DC motor (i.e., a rectified DC source having an AC component) addresses these problems since the AC component of the power source does not degrade the performance of the series connected motor. Accordingly, a smaller, more efficient motor can be used and noise levels and space requirements are reduced.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.